MoarVM's struct MVMCollectable's flags is now flags1 and flags2

As part of the fix for the data race described in MoarVM/MoarVM#1336
the flags member of struct MVMCollectable needs to be changed from a
single MVMuint16 to two MVMuint8 values. As `p6setfirstflag` and
`p6takefirstflag` directly manipulate this struct, they need to be
updated to reflect the changes.

Implemented with conditional compilation so that it will work with MoarVM
before and after these changes. Once MoarVM is updated, the conditional
compilation can be removed.

src/vm/moar/ops/perl6_ops.c

@@ -172,7 +172,11 @@ static void p6stateinit(MVMThreadContext *tc, MVMuint8 *cur_op) {
 }
 
 /* First FIRST, use a flag in the object header. */
+#ifdef MVM_COLLECTABLE_FLAGS1
+#define RAKUDO_FIRST_FLAG 128
+#else
 #define RAKUDO_FIRST_FLAG 16384
+#endif
 
 static MVMuint8 s_p6setfirstflag[] = {
     MVM_operand_obj | MVM_operand_write_reg,
@@ -181,7 +185,11 @@ static MVMuint8 s_p6setfirstflag[] = {
 static void p6setfirstflag(MVMThreadContext *tc, MVMuint8 *cur_op) {
     MVMObject *code_obj = GET_REG(tc, 2).o;
     MVMObject *vm_code  = MVM_frame_find_invokee(tc, code_obj, NULL);
+#ifdef MVM_COLLECTABLE_FLAGS1
+    vm_code->header.flags1 |= RAKUDO_FIRST_FLAG;
+#else
     vm_code->header.flags |= RAKUDO_FIRST_FLAG;
+#endif
     GET_REG(tc, 0).o = code_obj;
 }
 
@@ -190,8 +198,13 @@ static MVMuint8 s_p6takefirstflag[] = {
 };
 static void p6takefirstflag(MVMThreadContext *tc, MVMuint8 *cur_op) {
     MVMObject *vm_code = tc->cur_frame->code_ref;
+#ifdef MVM_COLLECTABLE_FLAGS1
+    if (vm_code->header.flags1 & RAKUDO_FIRST_FLAG) {
+        vm_code->header.flags1 ^= RAKUDO_FIRST_FLAG;
+#else
     if (vm_code->header.flags & RAKUDO_FIRST_FLAG) {
         vm_code->header.flags ^= RAKUDO_FIRST_FLAG;
+#endif
         GET_REG(tc, 0).i64 = 1;
     }
     else {